The purpose of this study is to establish a rationale for the selection and use of currently available immunosuppressive agents based on the modifying effects they exert on the purine metabolism of biochemically defined immunocompetent cells. We propose to define differences in purine metabolism between lymphocyte subsets differentiated by Wrights stain morphology, cell surface markers and in vitro immune function. These techniques will then be used to characterize cells infiltrating the Roberts and Hayry sponge matrix model of allograft rejection and to correlate the immunologic and biochemical effects of purine analogs, steroids, and Cyclosporin A on these cells. Initial studies will use spleen cells from genetically defined mice. Ficoll-Hypaque separation of mononuclear cells followed by plastic adherence and nylon wool separation will be used to obtain adherent, non-adherent, and B-cells. Non-adherent cells will be further separated by "panning" for T-cell subsets using anti-mouse T-cell reagents adsorbed to plastic dishes. Ideally, a fluorescence activated cell sorter will be used when available. Antigen specific cytotoxic cells will be recovered on monolayers of fibroblasts syngeneic with the immunizing allogeneic strain. Cytotoxicity, suppressor, and helper function will be assessed (using standard techniques of mixed leukocyte culture, cell mediated lympholysis, and cell addition studies) to confirm the selectivity of separation techniques and evaluate specificity for the immunizing antigen. Substrate consumption and product formation of the purine enxymes adenosine deaminase and purine nucleoside phosphorylase will be measured at various times after incubation of lymphocyte subset lysates with radiolabeled adenosine and inosine. Radiolabeled nucleosides will be quantitated after separationof microBondapack C18 columns using a reverse phase mode of high pressure liquid chromatography and labeled nucleotides will be quantiated after separation on a Partisil-10 SAX column.